Selective control and indication system



May14, 1946. A. B. MILLER SELECTIVE CONTROL AND INDICATION SYSTEM 0 Filed July 1'7, 1943 HIS ATTORNEY KB E E QQQN w vfik |l Patented May 14, 1946 L AND INDICATION YSTEM 7 Alfred B. Miller,,Edgewood, Pa., assignor to The Union Switch & Signal Company, Swissvale,

' f sELEcT vncon 'm Pa., a corporation'of Pennsylvania Application July 1943, Serial No. 495,231 7 claims. (Cl. 177-353) My invention relates to selective control and indication systems, and more-particularly to apparatus for individually'controlling and indicating a plurality of electric equipments.

It is frequently required i to selectively control 7 a plurality of devices having similar electric equip-1 ments from a remote control point, and to selectively indicate the conditions -of such'devices at the control point. When such devices are .not easily accessible it is desirable that the equipments of the different devices may be tested from time to time by anoperatorat the control point to determine the operative condition of each equipment. Also, it is in the interest of simplicity and economy that these services be accomplished through a single line circuit, Furthermore, in such a system,- accuracy of selection, reliability of operation and non-interference due to foreign energy are important.

Accordingly, a feature of my invention is the provision ofapparatus for a selective control and indication system incorporating novel and improved means to selectively indicate at which one of a plurality of devices a given eventoccurs and to control that device either automatically in response to such indication or to control the device manually as an operator may see lit, in response to such an indication.

Another feature of my invention is the provision of apparatus of the type here involved in corporating novel means Wherewith the probability of operation by energy from any source contemplated incorporating novel means for resetting and at times avoiding an operation of the apparatus.

A peculiar feature of my-invention is the provision of noveland improved indication and control means for a mine field and wherewith amine is fired either automatically in response to the approach of a vessel to the mine or may be fired manually as an operator may see fit in response to an indication of the approach of a vessel to the mine.

Other features, objects and. advantages of my invention will appear as the specification progresses.

The above features, objects and advantages of my invention will appear as the specification progresses. y a l The above features, objects and'advantages of my invention are attained by using currentsof different characteristics for indication, control and operation of each device of a group of similar devices. Each device is provided with an electric equipment characterized to be individual to the respective device, and the several equipments are'connected in multiple to a single transmitting or line circuit extending from the location of the devices to a remote control office. -A source of direct current of suitable voltage and a source of alternating current which may be of the usual 60 cycle commercial frequency are connected to the line circuit at the office to'constantly supply power to the different equipments. Each equipment is provided with an indication oscillator.

rent and each such oscillator supplies to th'e line circuit an indication alternating current of a frequency preselected for the individual device. Each such indication oscillator has associated therewith a control or detector unit whichis influenced in response to a predetermined condition at the device to modulate the indication current with two distinctive characteristics, such characteristics being preferably an increase in the amplitudeof the current followed by a decrease in the amplitude, or vice versa. Thus the line circuit is normally supplied with power and is excited with'different indication currents, one for each device of the group, and any one or more of which indication currents may carry distinctive characteristics.

The ofiice is provided with indication apparatus or indication receivers, one for each device, and the several receivers are connected in multiple to the line circuit through individual filters. Each such filter is tuned to pass only current of the frequency of the indication oscillator of the respective device. Each indication receiver is characterized by being responsive in one sense in response to the first modulation characteristic of L the indication current, and is responsive in a secand sense in response to thesecond modulation lator, and through which switches the oscillators,"

are connected to the line circuit and are made active or inactive. Thus the closing of any control switch and said other switch serves to supply to the line circuit an individual control current and the operating current simultaneously.

For automatic control, the ofiice apparatus is provided with indication relays, one for each device, and a group of interconnected relays. Each indication relay is governed by the indication receiver of the respective device, and in turn governs the operation of the group of relays. An indication relay and'the group of relays when operated connect the control oscillator of the same device as the indication relay and the operating oscillator to the line circuit simultaneously.

. To assure accurate selection, reliable operation and non-interference due to foreign energy, the equipment of each device includes control and operating means comprising a transformer, two filters, a relay, three ionization type of electron tubes, two condensers which serve as a secondary source of energy and an operating unit. The transformer and filters are connected in multiple to the line circuit through a blocking condenser to avoid energization thereof due to the direct current supplied to the line circuit. The transformer is designed for effective transfer of 60 cycle alternating current, that is, the power current. One filter is tuned to pass current only of the frequency of the control oscillator of the respective device, and the other filter is tuned to pass current only of the frequency of the operating oscillator. Energy passed by the first mentioned filter serves to break down a first one of the electron tubes and energize the relay by current supplied from the transformer. Energy passed by the second mentioned filter serves to excite a second one of the electron tubes if the relay is energized. Such operation of the tubes and relay connects the condensers to the transformer to be charged by the power current and when charged these condensers in series serve to excite a third one of the electron tubes to break down that tube. The third tube on breaking down connects the condensers to the operating unit, and the operating unit is actuated due to the discharged energy from the condensers. It follows that for actuating the operating unit of a device, the control and operating currents, as well as the 60 cycle poWer current, must be present on the line circuit.

I further provide at the office cancelling switches by which an indication of a device may be cancelled or reset without an operation of the device being efiected; Also test switches are located at the ofiice through which an operator can test the equipment of a device Without anactual operation of the operating unit'of the device. Furthermore, the oflice includes means wherewith' indication and operation of a device cannot be initiated due to an operation of some one of the other devices.

I shall describe one form of apparatus embodying my invention and shall then point out the novel features thereof in claims.

The accompanying drawing is a diagrammatic view showing one form of apparatus embodying my invention when used to indicate, control and fire the mines of a submarine minefield. It is to be understood that the invention is not limited to mine fields, and this one use serves to illustrate the principle of the invention. Furthermore, it is to be noted that that portion of the apparatus used for indication may be used independent of that portion of the apparatus used for control and operation, and vice versa.

. Referring to the drawing, the dash-dot rectangles MI and M2 represent two mines of a mine field protecting a harbor, only two mines MI and M2 of the field being shown for the sake of simplicity, since the mines are all alike and two are suflicient for a full understanding of the invention. The reference character OF designates a control office on shore in the vicinity'of the harbor that is defended by the mine field. The office OF and the mines are connected bya transmitting or line circuit comprising a single conductor cable LI and the ground path. Conductor LI extends from the oflice to a distribution point DP conveniently located withrespect to the mine field, and from which point a single conductor cable similar to cable LI extends to each mine, the cables to mines MI and M2 being identified as cables LSI and LS2, respectively, while a third broken cable LS3 extends to a third mine, not shown. Fuses Ill and II are interposed in cables LSI and LS2, respectively, at the distribution point for reasons to appear hereinafter. As stated above, one side of this line circuit is completed through the ground path, but a metallic conductor can be used.

Each mine is provided with an electric equipment through which the approach of a vessel is indicated and the mineis fired and tested. The mine equipments are alike except for the tuning of the circuits, and a description of the equipment for one mine will serve for an understanding of all. For this reason, the drawing discloses the equipment of mine MI, and mine M2 is shown conveniently in order to not unduly complicate the drawing.

The equipment of mine Ml comprises as essential elements an indication oscillator having a control or detector unit associated therewith, a power transformer, control and operating means, an .operating unit and testing means. The indication oscillator shown conventionally at M0 may be of any one of several types, but preferably is of the electron tube type. The specific structure of such oscillator forms no essential element of my invention, and it is suflicient for this application to point out thatthe filament circuits for the tubes of the oscillator are heated by current from a secondary winding I2 of a power transformer TI receiving power from the line circuit in a manner to appear shortly, and the plate circuits of the tubes of the oscillator are energized by direct current received from the line circuit through a connection including'inductance l3 and ground electrode I4, the direct currentbeing suppliedto the line circuit ina manner to be explained later. When thus powered, the oscillator MCD supplies to the line circuit through a connection including ar'condenser l5 and ground electrode I4, an alternating current of a frequency preselected for mineMl. For example, this in- 'operatingcurrent; and by way of illustration I shall assume the frequency of the operating currnt to be 1000 cycles per second.

dication current for mine Ml may be of a frequency of 10,000 cycles per second and would be of a substantially constant amplitude as long as the oscillator is powered in the manner just explained.

A control or detector unit'DU associated with oscillator M may take different forms and may be of the magnetic type, and the construction of such unit is disclosed only to the extent required for a full understanding of my inventionsince its construction forms no'part of my invention. A magnetizable core I6 is provided with a' winding ll connected to oscillator M0 through wires l8 and l9. Whena magnetizabl body, such as, for example, a vessel with a steel hull approaches the unit DU, it is magnetically influenced to control the output of theoscillator, the amplitude of the output of the oscillator being made to first increase and then decrease, or vice versa, at a rate predetermined in part by the 'proportioning of the partsof the apparatus. That is to say, the unit DU may control the coupling or bias of the tubes of the oscillator to vary the amplitude of the output of .the oscillator in response to a magnetic influence. Hence, under normal conditions, that is, when no vessel is present, oscillator M0 supplies to the line circuit an indication current of a frequency individual for mine MI, and of a normal amplitude, but when a vessel is present, the amplitude of the indication current increases and-then decreases, or vice'versa, and such variation in amplitude takes place at not less than a preselected rate. In other words,

the indication curren'tis at times modulated to have two distinctive characteristics which follow each other within a predetermined interval.

TransformerTl is a power transformer having a primary winding 22 connected across the line circuit through a blocking condenser 24, and ground electrode .25, to receive Power from a source of alternating current connected to the line circuit at the office, as will later be pointed out. Transformer TI is provided with a secondary winding 23 as well as secondary Winding l2 referred to hereinbefore, winding 23-being pro vided with different terminals designated by the numerals l, 2, 3 and 4 to furnish power at different voltages to the control and operating portion of the equipment. I

The control and operating means of the min equipment comprises filters Fland F2, a relay A, electron tubes Vl, V2 and V3 and condensers Cl and C2. Filter F2 includes a transformer26 and condensers 21 and 28, the primary winding of transformer 26 in series with condenser 21 being connected across the line circuit through blocking condenser 24 and ground electrode 25, and secondary winding 29 of transformer 26 and condenser 28 in multiple being connected to a control electrode 30 and cathode 3lof tube Vl. Filter F2 is tuned to pass current only of the frequency preselected for the control current of mine MI, and by Way of illustration I shall assume that this control current for mine Ml is of the frequency of 5000 cycles per second.

Filter Fl includes a transformer 32 and condensers 33 and 34, primary winding 35 of transformer 32in series with condenser 33 being connected across the line circuit through a portion of primary winding 22 of transformer TLand blocking condenser. 24, and secondary winding 36 of transformer-32 and condenser 34 i multiple being connected to control electrode 3'! and oath;- ode 38 of tube V2. Filter Fl is tuned to pass current. only of the frequencypreselected for the Tube Vl'is a cold cathode gas filled tube, the anode 39 and cathode 3| of which are connected througha winding of relay A to terminals l and g4 of'secondary winding 23 of transformer Tl, as

will be clear-by an inspection of the drawing, the voltage thus applied to the anode of tube Vl being however," insufficient to break down the and retained energized during the negative half cycle of the power current supplied from transformer Tl' due to a condenser 40 connected across the Winding of-relay A. I

Relay A is a bias polar relay and is operated to its reverse position,'that is, the position opposite that I shown in the drawing when energized by 'the'currentpas'sed through tube VI. With relay A operated to close its'revers'e contact 4|, condue to the 60 cycle'power current from the line .ment of the equipment.

Tube V3 is likewise a cold cathode gas filled circuit, the voltage of the charge built up on condenser Cl being preselected according to the position of terminal 2 of secondary winding 23. The energy thus stored in condenser Cl serves as a secondary source of power for operating the operating unit-as will appear shortly.

Tube v2 is also a'cold cathode gas filled tube and is provided with an anode circuit connected across terminals 4 and l of secondary winding 23 of transformer Tl, such-circuit extending from terminal 4 through a resistor R2, condenser C2,

anode 44 and tube space to cathode 38 of tube V2, and contact 43 ofrrelay A to terminal I of secondary winding 23. Hence, when relay A is energized to close contact 43 and operating current is passed from the line circuit through filter Fl to excite the control electrode 31 of tube V2,

tube V2 breaks down and condenser C2 is charged by the half cycles'of the power current that makes terminal 4 of transformer Tl positive, the voltage 'of condenser C2 being preselected according to the proportioning'of:secondary winding 23 and re- -sistor;R2. The charge. thus built up on condenser C2 serves as an additional source of secondary energy to be used for operating the operating eletube having aicontrol electrode 45 connected to termin'al3 of secondary winding 23 and its cathode 46 connected to terminal I through a path including tube V2 "and contact 43 of relay A. Hence when the relay A is energized and tube V2 is made conductive, vthe tube V3 is excited from terminals With condescribed, the voltage" acros the condensers Cl and C2 in seriesis applied across the anode 4! and cathode'46 oftube V3 to'break down that tube dueto the excitation of the control electrode 45;and with tube-V3 made'iconductive, the charge :on condensers Cl-and .-C2 causes current to flow throughan elementi48'ofthe operating unit D0 which? is a detonator'for the mine.

This discharge current through the element 48 of the detonator ofthe mine is suflicient to cause the firingof the mine.

;;The equipment formine MZand for eachof 1the othenmines of thermin'ezfield.isrsubstantially the same as thatsjust described for mine Ml,

alternating current, these two sources'of current being permanently connected to the line circuit,

and as disclosed the direct current source is a battery OB of proper voltage, itspositive terminal B250 being connected-to conductor Ll througha choke coil 20 and its negative terminal C250 being connected to a groundelectrodeil. The'source of power alternating current is'a'tr-ansformer T2, the primary winding of which is connected to terminals Eli and CX:ofa:suitablesource, such as "a generator, not -shown, and the secondary winding of which has one terminal'connected to line conductor 'Ll through a line filter=LF--and its other terminal connected to ground electrode-Z l.

The indication means may take different forms and preferably includes an individual receiver for each mine, the-indication receiversRAl and RA2 for mines MI and M2,-respectively, being shown in the drawing. Preferably, each indication receiver is of the construction disclosed an'd claimed in a copending application Serial No. 494,183,

filed July 10, 1943, by W. P.Place forElectrical "control and indication apparatus, and to-which application reference ismade for a full understanding of such indication apparatus-and it is sufficient for this application -to describe such indication receiver or apparatus-'butbriefly. Indication receiver :RAI forimineMl is connected to the line circuit through a filterr5fl of any wellknown arrangement, the partszof such filter bein proportioned'to pass alternating current only of the frequency of theindication current supplied by the indication oscillator "MO of mine-Ml; and

which current I have'assumedfor illustration to be of 10,000 cycles'per second, Theenergy passed by filter 50 of receiver RA! is applied to'a rectifier-detector 5|, which includes two gas ifille'd tubesbiased in sucha manner'that I an increase in the amplitude of the received indication'current causes one tube to break down and illuminate a first indication lamp -52, and a'decreasein'the amplitude of the indication current causes the other gas filled tube to breakdown and illuminate a second indication lamp 53. According'to my invention, a winding of an indication relay IKI is interposed in the common'portion'of the circuits of lamps52 and 53, the circuit being traced from terminal Bl of a suitable source-"of direct current such as a battery not shown, through winding 54 of a transformer T3, back'conta'ct 55 of a .relay CO to be referred to later, normally closed contact 56 of a manually operable cancelling switch'lS3, top winding of relay lKljlamps 52 and 53 and the respectivegas'filled tubes in multiple to the otherterminalofthe same source ofcurrent. Relay IKI is a bias polar relay and is adjusted so that when it is energized "by the current flowing when both lamps-52 and'53 are illuminated, the relay is operated against its bias to the left-hand position .as viewed' inlthe drawing, but when current for onelamp only flows,

aaoogaco -With -a stick circuit which-extends 4 from terminal "Bl, ithrough back contact 51- of a relay RS and the-winding of a repeater relayKP'of a group of relays 'to-be described shortly, normally closed contact 58 of the cancelling switch I53, reverse contact 59 of relay IKI, and lower winding of relay 1K! to terminal CI of the same source of current. It follows that operation of relay lK! in responseto the illuminationof lamps 52 and ='53,:due to variations in th indicationcurrent received'from theline circuit, causes relay IKI tobe retained in its operated position through its stick circuit-until suchitime as the stick circuit is opened either at back contact 5'! of relay RS or contact 58 o'fswitch I83.

An indication relay 1K2 is'associated with the indication receiverzRAZformine'M2 in the same manner as relay .lKl ..is associated with the re- CGlVGII'RAI The'indication means also includes an'audible indicator in the .form of a bell or gong (i0, and which is controlled through "transformer T3 and a gas filled tube 6|. Control electrode 62 and cathode 63 of tube'lil arerconnected across secondary winding of transformer T3, and bell 150 is connected in an' anode circuit which is connected'to the Bl'Cl current source and to a condenser 65. Normally condenser 65 is charged from the battery *Bl-Cl through a resistor 66, the charge on the condenser beingsubstantially the full voltage of the'battery. When either lamp '52 or 53 is illuminated, the surge of current through the primary winding of transformer T3 induces an electromotive force in secondary winding 84 to excite tube SI, and which tubes breaks down'under the influence of this excitation and'the voltage of condenser 65 and condenser 6'5 discharges through bell and the tube 'to cause the bell'to sound,'the voltage from source BI-Cl through resistor 66 being insufficient to retain the'tube conductive.

The indication means also includes an auxiliary indication lamp for each mine, and which auxiliary'lamp serves as a permanent record that a mine has been firedv Such a lamp 61 is provided for mine MI and lamp 6'! is controlled by indication relay IKI and a cold cathode gas filled tube 58. The anode circuit for tube 68 includes terminal BI, lamp 61, anode 69 and tube space to cathode 10, a push button H and terminal CI.

The control electrode" of the tube is connected 'to terminal Bl through lamp 61, and is connected to cathode '10 through a shunt path including resistor 13 and the normally closed contact 1d of relay IKI. 'When relay IKI is operated to open contact 14 inresponse to an indication current .from mine Ml, tube 68 is excited and becomes the relay is not energized sufiiciently to operate its contacts. Indication relay JKI is provided conductive so that lamp 6! is'illuminated. Subsequent to such operation of relay lKl the tube -68 remains conductive so that the lamp 6'! remains illuminated until such time as the push button 1! 'is-operated'toopen the anode circuit.

The manual control means includes a control oscillator and an associatedmanually operable switch for each mine, together With an operating oscillator that is common to the entire "group of mines.

*lator is-immaterial and oscillators Al, A2 and "AF, as well as all other oscillators, are preferablyof 'the 'electron tube type. Closin of switch SI toconnect terminal B250 of the oflice source of direct current to oscillator Al through wire 15 serves-to energize that oscillator and it is made active to supply control current of a frequency individual for mine MI, and which frequency I assumedhereinbefore to be of 5000 cycle per second. The output side of oscillator .Al is connected across the line circuit by one of its output terminals being connected to: conductor .Ll through wirelfi andkcontact 11 of switch ISI and its other output terminal being connected to groundelectrode 18., Similarly,

operation of switch S2 renders control oscillator the tubes. are deionized so that the lamps 52' and 53. are extinguished, relay Kl remaining in its reverse position due to' its stick circuit. With relay C0 picked up to close front contact 80 current flow from terminal BI through switch MS, contact as of relay KP, front contact B0 ofrelay C0 and winding of firing relay A2 for mine M2 active. Operation of switch IS! to close contact 19 connects terminal B250. to the operating oscillator AF and that oscillator isrendered active to supply current of the frequency selected for the operating current, and which frequency I have assumed hereinbefore to be of the order of 1000 cycle per second. Also the closing of switch lSlconnects the output side of the oscillator AF to the line circuit in multiple with the output of oscillator AI. It is clear, therefore, that simultaneous operation of switches SI and IS I causes control oscillator Al and operating oscillator AF to becomeactive and supply current to the line circuit. 7 v

The automatic control means includes a master switch MS, a. group of interconnected relays KP, CO, F and RS; an operating oscillator lAFand individual control oscillators IAI IAZ, etc., a control'oscillator for each mine. Operating oscillator IAF is of the same construction as oscillator AF of the manual control means, and likewise the control oscillators IAI and IA2 are similar to the control oscillators AI and A2, respectively. It i believed that this automatic control means, .as well as the reset and'testing.

means of the office. apparatus may best be understood froma description of the operational the apparatus; it being pointed out that theautomatic control apparatus is made active when the master switch MS is set at the position illustrated by a solid line, and is made inactive when the switch MS is set at the position illustrated by a dotted line. r

Normally, that is, when no vessel is approaching the mine field, the apparatus is positioned as shown in the drawing, and the indication oscillator at each mine is active to supply .current of an individual frequency to the line circuit, each such indication current being of a normal amplitude; that is, it is non-modulated I shall assume that the master switch MS is set at its full line position to actively condition the automatic control. apparatus, and a vessel-Lap:

proaches'mine Ml to influence its control .unit DU for modulating the indication current of that mine, the amplitude of the currentbeing increased and then, decreased with respect to.

its normal value." Such modulation of the indication current is indicated at the office by the two lamps 52 and 53 being illuminated, and the indication relay IKI being operated, the gong or bell 00 being momentarily sounded, first when lamp 52 is illuminated and then again when lamp 53 is illuminated. Operation of relay IKI closes its stick circuit and also initiates an. automatic firing action for the mine; Repeater relay KP is energized when the stickcircuit for relay IKI .is completed. Relay KE! is a bias polar relay and when thus energized it is op-' erated to its reverse position to close contacts 88 M and 89. from terminal Bl through master switch MS With contact 88 closed, current flows F to terminal BI, and relay F is energized. The picking up of relay F to close front contact 83 completes a circuit for supplying-current from terminal B250 of battery OB to the operating oscillator IAF, and that oscillator is made active, its operating circuit being completed ,through ground electrodes 84 and 2l.- Current also flows from terminal B250 through front contact 83, reverse contact 86 of indication re,-

lay IKI, operating circuit of the control 'oscfi lator IAI, and ground electrodes 84 andn zl to terminal C250, and the control 'oscillatorzlAt is rendered active. The output sides of, both oscillators IAF and [Al are connected acrossthe line circuit through front' contact 85 of the relayF and'ground electrode 84.- With'both operating current and control current thus supplied to the line circuit simultaneously,current is'passed by the two filters Fl and-'Fzof the equipment of mine MI, and the mine is fired due to the energizing of 'thedetonator infthe manner explained in detail hereinbefore 'The picking up of relay F to close 'front contact 8! complete an obvious circuit forenergizing re.

lay RS and that relay is picked up at the end KP deenergizes the firing relay F 'and'that re-V lay is released to open front contacts 8i, 83 and 85. The opening of front contacts 831and85' removes'currentfrom the oscillators and disconnects their output sides from the line circuit. vThe opening of front contacts]; causes relay RS to be deenergized, and relay RSis re:

leased to open front contact 82 in the stick circuit of relay C0, which latter relay is then re:-

leased and the firing action is completed and the relay group is made in readiness to automatically fire any other mine that becomes indicated through its respective indication appa-' ratus. V

When mine MI is fired, the mine, end of cable LSI is torn loose and becomes grounded causing an excessive current to flow from battery OB and the transformer T2 with the resu ltcthe fuse I0 interposed in cable LSI at the distribution point DP blows and frees the system from the cable of the fired mine. I

It is to be noted that lampG'l is illuminated when indication. relay IKI is operated in response tothe approach of the vessel to mine MI, and remains illuminated as an indication or permanent record ,of the firing of this mine as explained above. Lamp 6! can, of course, be extinguished by the operator using push button H to open the anode circuit for tube 68.

When mine MI is fired the control unit DU for mine M2 may be influenced in such away as to cause the indication current for mine. M2 to be modulated as ifa .vessel was approaching the mine. This modulation of the indication current would be received by the indication receiver RA2 and would tend to bring about the energization of indication relay lKZ. However, the automatic firing action started due to operation of indication relay lKl for mine Ml causes relay CO to be picked up to open back contact 55, removing current from the control circuit for relay lK2, and all other indication relays. Thus, since relay CO is retained energized during the entire automatic firing action for mine Ml, and which action may be made relatively long due to the slow pick-up period of relay RS, the indication oscillator at mine M2 would stabilize at its normal condition and remove excitation from the respective indication receivers before the firin action for the mine first indicated is terminated, and firing of a mine due to the firing of an adjacent mine is avoided.

I shall. next assume that the apparatus isatJa normal condition with master switch MS .inthe position illustrated-by the dotted line, so that the automatic control means ismade inactive, and manual firing'of a mine. is reliedupon. A vessel approaching mine Ml brings aboutmodulation of the indication current and the actuation-. the

indication lamps 52 and 53 'at the office together 1 with operation of relays lKl and KP in the manner already explained. Operation of relays lKl and KP serves no useful purpose at this time ex.

cept tobring about the illumination of lamp 6],

which would serve as a record that. mineMl has been indicated. With lamps 52 and 53 illuminated to indicateithe presence of avessel near mine Ml, the operator can fire mine Ml bysimultaneously closing switches SI and lSl toren'derx.

about the firing of a mine at anytime irrespective of the indication apparatus by closing theproper control-oscillator switch and switchlSl.

Under manual control and indication for mine Ml would-be cancelled by the operator actuating. switch IS3 to open the circuit for. deionizing the tubes of the indication receiver andto openthe stick circuit for the indication relay.

In the event mine M2-orany other mineof the field should become indicated due to manual fir.- ing of mine Ml, such indication-of mine MZcan be cancelled by the operation of switch LS3, as explained hereinbefore.

Provision has been made for periodically testing the individual mine equipments. to see that they are in proper working condition. To test. mine Ml, for example, the switch Sl would be closed to render the control oscillator Al active as already explained. A switch lS2 would then be closed to connect the output of the oscillator Al to the line circuit. This control current thus supplied to the line circuit would be passed by. filter F2 to excite tube VI and energize relay A of the mine equipment. Switch ISZ. would then be released to remove the control currentfrom the line circuit causing tube V! to'be deionized and. relay A restored to its normal positionby the bias feature of the relay. Such momentary operation of relay A'to opentits contact in opens a shunt around resistor 'fie- 'of the indicationoscillator MO, and oscillator MO is controlled-in such a manner that the double modulation of the output of the oscillator is effected. That is, the amplitude of the oscillator MO" is made to increase and then decrease-similar to thevariations effected through unit DUI This .doubl var-iation of theamplitude of the'indication current controlsthe indication receiver RAlthereby completing the indication. The indication eifected-through this-test would be cancelled byoperation of switch lS3 and by oscillator Al being restored to its inactive condition by opening switch Sl. Each of the other mines may be tested ina similar manner.

It is to be understood that although I have assumed for the purpose of illustration definite frequencies and voltages for the different current sources, the invention is not limited thereto, and other frequencies andvoltages can be used;

Apparatus here disclosed has the advantages that the circuits are safe to a high degree in that no failure-of anypart of a circuit can cause the firingofa mine. The-circuit elements are-of a construction that a high degree-of reliability is achieved and sufficient frequency margin can be provided for selective control and indication-of a relatively large group of mines within reasonable frequency bands;

Although I have" herein shown and described but one form of selective control and indication systems embodying my invention; it is understood that various changes and modifications may be made therein within" the scope of; the appended what I across'said line circuit to supplyicurrent thereto,

means including a controller to at'times' connect said control source'ofcurrent across said circuit to supply current thereto simultaneously. with said power current, a transformerand a filter atsaid'remote point connected inmultiple across, saidlin'e circuit, a relay, a,gas filled tube .having ananode circuitconnectedtoa' secondary winding of said transformer through ,a winding of said relay but normally ineffective to breakdown the tube, means including said filter to connect a contr'ol'electrode of said'tube to said'line circuit and said filter tuned to pass current only of saidsecond frequency to break down said tube when saidcontrolsource is connected to said line circuit, a condenser, means including an operated contact of said relay an'da rectifier to connect said condenser to a secondaryv winding of said transformer to store energy inthe condenser, and an operating unit effectively connected at times to the condenser to operate tlieunitbysuch stored energy.

2. In combination, aline circuit, supply means including a source of control alternating current of a first frequency and'a source of operating current of a second frequency and both connected at times across said'line. circuit to supply said two currents simultaneously, a first filter tuned to pass current only of. said: first frequency; a second" filter tun'ed' topass current only ofisaid second frequency, a relay; another'source' ofcurrent, a, gas filled tube having an anode circuit includinga windin .of said relayand saidother current, source but ineffective to. breakdown the tube, circuit means including said first filter to connect a control electrode of said tube to said line circuit to breakdown the tube and energize said relay in response to said control current, a first condenser connected to said othersource through an operated contact of said relay to store energy in said first condenser, another gas filled tube having an anode circuit including a;

second condenser and said othersource but, in effective to break down that tube, other circuit means including said second filter to connect a control electrode of said second tube to said line circuit to break down said other tube in response tosaid operating current to store energy insaid second condenser, and an operating means connected at times to said condensers and operated by the energy thus stored therein.

3. In combination, a line circuit extending from an ofiice to a, remote point; ofiice sup-ply means including a first,'a second and a third source of alternating current of a first, a second and a third frequency respectively; said first source connected to said line circuit, means including controllers to at times connect said second and third sources to said line circuit simultaneously, a

transformer and a first and a second filter connected to said line circuit at said remote point, said first and second filters tuned to pass only currents of said second and third frequencies respectively, a relay, a first gas filled tube having an anode circuit connected to a secondary winding of said transformer through a winding of said relay but normally ineffective to break down that tube,'means including said first filter to'connect a, control electrode of said first tube to said line circuit to break down that tube and energize said relay in response to said second current, a second gas filled tube having an anode circuit connected to a secondary winding of said transformer but normally ineffective to breakdown that tube, means including said second filter to connect a control electrode of said second tube to said line circuit to break down that tube in response to said third current, and operating means receiving energy from said transformer through a contact of saidrelay and said second tube when it is thus made conductive.

4. In combination, a line circuit extending from an oifice to a remote point; office supply means including a first, a second and a third source of alternating current of a first, a second and a third frequency respectively, and which sources are at times connected to said line circuit simultaneously, a transformer and a first and a second filter at said remote point and connected to said line circuit, said first and secfilled tube having an anode circuit connected to a secondary winding of said transformer but normally ineffective to break down that tube, means including said second filter to connect a control electrode of said second tube to said line circuit to break down that tube in response to charge that condenser, a third gas filled tube.

having an anode circuit connected across said condensers in series through an operating unit, and. acontrol electrode of said third tube con- 103 nectedto said transformer through said second tubetobreak down said third tube and operate saidoperating unit by the charge thus created on. said first and second condensers.

,5.:In combination, a line circuit extending loifrom an oifice to a remote point, supply means including a source of direct current connected to said circuit at said office, an oscillator at said remotepointconnected across said line circuit, said oscillator powered in part at least by said direct current to supplyvto the circuit at times an alternating current of a preselected frequency and preselected characteristics, an oflice indication receiver' connected to said line circuit through a filter tuned to pass current only of 26 said preselected frequency, said receiver having an output circuit including an indication relay which is effectively energized in response to said characteristics of the indicationcurrent, a first and a second ofiice oscillator to supply currents 80 of a first and a second frequency respectively but both normally deenergized, another relay controlled by said indication relay, circuit means including front contacts of said other relay to energize said first and second oscillators and 86 to connect the outputs of these oscillators across said line circuit, a control and an operating means at said remote point, said control means connected to said line circuit through a filter tuned to pass only current of said first frequency, 40 said operating means connected to said line circuit through a filter tuned to pass only current of said second frequency, and an operating unit governed jointly by said control and operating means and effectively energized only when the control and operating means receive current simultaneously.

6. In combination; a line circuit extending from an oifice to a remote point, a plurality of devices at said remote point and each provided with an indication oscillator connected to said circuit and normally active to supply an indication current of a frequency preselected to be individual for the respective device, detectors one for each said oscillator and each said detector a predetermined modulation on the respective indication current, indication receivers at said ofiice one for each said device and each receiver connected to said line circuit through a filter tuned to pass only current of the frequency of the oscillator of the respective device, indication relays one for each said receiver and each such relay connected to its receiver to be energized in response to said modulation of the respective relays, a repeater relay having a winding common to said stick circuits, an office operating oscillator to supply current of a preselected frequency, office control oscillatorsone for each said device and each control oscillator to supply current of a frequency made individual for the respective device, ofiice circuit means controlled by said repeater relay and each said indication relay to connectsaid operating oscillator and the control oscillator for the same device as the indicaconnected to its oscillator to impress at times indication current, a stick circuit for each of said i,

tion relay to said line circuit, and-control and; operating means at each of said devices con'-.

nected to said line circuit and efiectively energizcd only when. currents of. said operating. free quency and. the respective control frequency are;

supplied to the line circuit simultaneously 7. In combination, a line circuit extending,

from an ofiice to a remote point, .a plurality of devices at said remotepoint and eachprovided.

with an indication oscillator connected to. said circuit and normally active tonsupplyl an;.indication current of a frequencypreselected tobe individual for the respective device, detectors:

one for each said oscillator' and eachisaidl detector connected to its oscillator to impressat times a predetermined modulation on the respectiveindication current, indication receiversat. saidoffice one for-reach said: device andeach receiver,

connected to said lineflcirecuit through a filter tuned to pass only current, of the frequency. of the oscillator. of the respective device, indication relays I one for. each said receiver: and eachsuch relayconnected to its rece'iver' to beener g-izedz in response-to'said modulation'of the respectiveindication current, a. stick circuit for each of said relays, a repeater relay having a winding common to said stick circuits, ofiice control oscillators one for each said devicesand each-control oscillator to supply control current of: a frequency made individual for. the respective device; office circuit means controlled by said repeaterrelay and each i ofsaid indication relays when energized to-- connect the control oscillator for the-same deviceas the indication relay to said 

